Almost all personal, commercial, industrial and military electronic devices have some type of electrical circuit board mounted to a housing. This is true for microstrip carrier boards, used to process microwave signals, that are housed in radio frequency processing boxes. Typically microstrip carrier boards, like other circuit boards, have been secured to the housing by screws that are fastened into threaded mounting bores in the housing.
Although screws have been used extensively to fasten circuit boards to housings, there are disadvantages associated with their use. It is relatively expensive to provide a housing with threaded mounting bores. When the circuit board is removed for repair or replacement, there is always the possibility that the bore threading will be stripped, making it impossible to refasten the circuit board to the housing. The possibility that this will happen increases if circuit boards are repetitively inserted and removed from the housing and the threading becomes worn. Furthermore, screw fastening is a labor intensive operation and dependent upon the skill of the operator.
There are also a number of reasons why screw fastening is an especially disadvantageous way to attach microstrip carriers to radio frequency processing boxes. Microstrip carriers tend to be miniaturized, and the boxes in which they are housed have a relatively thin profile. Since the mounting bores are small, the relative cost of tapping them so they are threaded is high. Furthermore, some boxes are too thin to allow for threaded bores of sufficient depth to accommodate screws that can securely fasten carrier boards.
Also, microstrip carriers are attached to connecting circuitry located in the radio frequency processing box. Usually, this connection is made by a solder bridge that should be as short as possible to minimize the impedance of the connection. The box mounting bores and carrier screw holes must be closely aligned to ensure that the carrier is secured in the box and the gap between the carrier and the connecting circuitry is as small as possible. This further increases the cost of the fastening connection since the location of the box bores and circuitry screw holes must be precisely machined.
Furthermore, tolerances between the screws and bores increase as the bore threading becomes worn with repeated carrier insertion and removal. This may make it difficult to securely fasten the carrier to the housing so as to maintain the solder bridge between the carrier and the connection circuitry.
A need therefore exists for an improved method for mounting a circuit board, such as a microstrip carrier, to a housing. The method should not rely on closely aligned bores and screw holes, should be compatible with relatively thin housings, and not be labor intensive or operator dependent. The new method of mounting should also allow for repetitive insertion and removal of the circuit board without impairing the integrity of the mount, and it should allow for the repetitive precise mounting of a circuit board to the housing. Furthermore, the new method of mounting should not require relatively expensive mounting fixtures for either the housing or circuit board.